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SRT Testing, Audio Encoder bitrate
Rank: Newbie
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Joined: 11/4/2019(UTC) Posts: 6  Location: Christchurch Thanks: 1 times
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Testing VMIX SRT to VMIX SRT over the weekend, Worked very well, much better than older Teradeks
50i Decklink SDI > 1080 50p VMIX Encode > SRT 720 50p 2.5mbit > 1080 50p VMIX Decode > 50i Decklink SDI
The Motion looked amazing, looked like interlaced content :)
I was on 23.0.0.21 HEVC Looked Noticely worse than H264
I've since upgraded to 23.0.0.22 and HEVC looks to be better
The Audio Encoder is defiantly not working properly
I was transmitting 4 Channels of audio,
is the audio bitrate shared with all 4 channels??
64kpbs sounds like 32kbps
128 sounds like 64kbps
256 sounds like 128kbps
I have test wavs at 64, 128, 256, 384
Can we get more control of the SRT encoder, ABR and VBR options
In addition TCP/WEB API control of the entire SRT encoder options
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Rank: Advanced Member
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Joined: 2/23/2017(UTC) Posts: 189  Thanks: 1 times
Was thanked: 52 time(s) in 42 post(s)
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Audio bitrate is shared. You can just use 512Kbps to achieve 128Kbps per stereo pair when streaming all 8 channels.
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 1 user thanked MartLeib for this useful post.
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Rank: Newbie
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Joined: 11/4/2019(UTC) Posts: 6 Location: Christchurch Thanks: 1 times
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Originally Posted by: MartLeib  Audio bitrate is shared. You can just use 512Kbps to achieve 128Kbps per stereo pair when streaming all 8 channels. This makes sense, many thanks
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Rank: Member
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Joined: 2/9/2019(UTC) Posts: 27  Location: Berlin Was thanked: 2 time(s) in 2 post(s)
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to add a question to this. Is there an upper limit for audio bitrate in SRT?
I am running tests with 8 Channel Audio and want them as HQ as possible.
It's pretty hard to tell right now what's the reason for the SRT connection not establishing.
Also: If I get this right I have BUS MABC as a stereo pair each. Are these Stereo Pairs somehow synched in SRT?
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Rank: Advanced Member
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Joined: 2/23/2017(UTC) Posts: 189 Thanks: 1 times
Was thanked: 52 time(s) in 42 post(s)
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I do not know regarding the upper limit, but no point to go over 320Kbps per bus. Totaling in 320 x 4 = 1280Kbps.
Your SRT video output is synced to all the audio buses you are sending.
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Rank: Member
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Joined: 2/9/2019(UTC) Posts: 27 Location: Berlin Was thanked: 2 time(s) in 2 post(s)
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Originally Posted by: MartLeib I do not know regarding the upper limit, but no point to go over 320Kbps per bus. Totaling in 320 x 4 = 1280Kbps.
Your SRT video output is synced to all the audio buses you are sending. Are you sure about that? Video is not even that important to me, but I need sample exact sync on the audio buses because I want to send multitrack music. My information is that even Haivision says in their Makitos there is no guaranteed sync between the audio channels.
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Rank: Member
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Joined: 3/26/2017(UTC)
Posts: 23
Was thanked: 3 time(s) in 2 post(s)
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Originally Posted by: Paul_WCP Originally Posted by: MartLeib I do not know regarding the upper limit, but no point to go over 320Kbps per bus. Totaling in 320 x 4 = 1280Kbps.
Your SRT video output is synced to all the audio buses you are sending. Are you sure about that? Video is not even that important to me, but I need sample exact sync on the audio buses because I want to send multitrack music. My information is that even Haivision says in their Makitos there is no guaranteed sync between the audio channels. I'm still searching for a high quality audio streaming setup where the video isn't as important as the audio. It seems to be always the other way around. So if I understand this correctly - SRT really compresses the hell out of the audio? Is there any technical details on this anywhere? What I would like is something like what Netflix use (on their audio side it's 640kbps) - or even non-compressed audio streaming raw. 48K + (prefer 96K) sample rates. Video can be 720p for all I care ;)
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